Ore is generally mined for the economically valuable minerals that can be extracted therefrom. In addition to the valuable minerals, ore also contains gangue minerals, which are waste products. The major classifications of minerals present in ore are native elements, sulfide and sulfo minerals, oxides and hydrated oxides, halogen minerals, nitrates, carbonates, borates, sulfate types, sulfite types and silicates. Iron, for example, may be present in the form of oxides, such as hematite (Fe.sub.2 O.sub.3) and magnetite (FeFe.sub.2 O.sub.4), or in the form of non-oxides, such as pyrrhotite (FeS), pyrite (FeS.sub.2), siderite (FeCO.sub.3), etc. In order to recover the valuable minerals of the ore, generally the ore is ground into fine particles and the valuable minerals are separated from the other minerals of the ore by a process such as froth flotation. In froth flotation, valuable minerals adhere to the froth bubbles and can be removed as part of the froth. The remainder of the minerals are not removed and so remain in an aqueous dispersion. This remainder is collectively called the tailings, which usually includes significant amounts of gangue minerals. Silicates such as quartz (SiO.sub.2) and clay minerals, when not mined as the valuable mineral, are also often present in significant amounts in the tailings. The clays that remain in the aqueous dispersion formed during froth flotation are difficult to separate from the aqueous dispersion because they absorb water. Accordingly, there remains to be developed an efficient method of separating such suspended solids of ore from the liquid of the aqueous dispersion that results from the flotation process.
In addition to froth flotation, it is known that iron oxide or tin oxide minerals can be separated as the valuable minerals from the other minerals present in the ore by selective flocculation using a hydroxamated polymer. In selective flocculation, macromolecules of the flocculent material are adsorbed by the particles to be flocculated. Hydroxamated polyacrylamide has been shown to selectively flocculate both iron oxide and tin oxide from other minerals. U.S. Pat. No. 4,902,751, is expressly incorporated herein by reference to the extent necessary to understand the polymers of the present invention. Similarly, Shankar et al. in Bull. Mater. Sci.; Vol. 10; pages 423-433 (1988) discloses that by using a hydroxamated polyacrylamide, synthetic iron oxide can be selectively flocculated from kaolin, a type of silicate clay mineral typically present in naturally occurring high alumina gangue content Indian iron ore deposits, when both are present in an aqueous dispersion. That is, the hydroxamated polyacrylamide was found to selectively flocculate the iron oxide minerals, but not the kaolin clay minerals. Hydroxamated polymers were further shown to be specific to iron oxide minerals by Spitzer et al. in U.S. Pat. No. 4,767,540, which discloses the use of hydroxamated polymers for flocculating red mud, an iron oxide mineral, in a process of separating the red mud from aluminate liquors produced during the Bayer process for purifying bauxite. Appleton et al. in Jour. So. African Inst. of Mining and Metallurgy; Vol. 76; pages 117-19 (1975) and Clauss et al. in Int. J. Miner. Proc.; Vol. 3; page 27 (1976) discloses that by using a hydroxamated polymer, synthetic cassiterite, a synthesized tin oxide mineral, can be selectively flocculated from quartz, a silicon dioxide mineral, when both are present in an aqueous solution. That is, the hydroxamated polymer was found to strongly adsorb on the cassiterite, but not at all on the quartz surface.
Presently, anionic polyacrylamides are generally used to flocculate dispersions of suspended solids having at least two minerals or suspended solids comprising primarily minerals other than iron oxide or tin oxide. However, the use of anionic polyacrylamides for such flocculation results in unpredictable settling and turbidity rates.
Therefore, a need exists for an efficient process for separating solids suspended in a liquid which solids have at least two minerals or primarily comprise minerals other than iron oxide or tin oxide.